There are many forms of catheter and the shapes and sizes are dictated primarily by use, requirements for insertion, whether the catheter is for long or short term use, and other similar factors. Within these many forms is a group of catheters which are designed to be entered into a blood vessel. Such intrusion is becoming increasingly more common as techniques and procedures for dialysis, angioplasty, and cardiac treatments improve. In such procedures the catheter is entered into the blood vessel using one of a number of different techniques.
A first of these techniques is known as a cut-down technique. In this procedure the tissue is parted and the blood vessel opened surgically to enter the catheter. Other techniques involve the use of a hollow needle. In one approach the needle is followed by a sleeve and the catheter is engaged within the sleeve which is then removed. Another technique was developed by Seldinger and this involves the use of a wire which is engaged through the hollow needle to guide the catheter into position.
Catheters in blood vessels should preferably have a configuration of tip portion which minimizes the risk of damage to the blood vessel. The portion is preferably shaped to have a reduced cross-section compared with the main body of the catheter and is configured with a less rigid section adjacent the tip to permit the catheter to flex to the shape of the blood vessel. It is not uncommon to arrange the catheter to have a main body of a first cross-section and a tip portion of a smaller cross-section so that on insertion the smaller cross section can be entered and act as a flexible guide for the larger cross-section.
When it is required to make a catheter with a smaller cross-section at the tip, it has become practice to provide a section of thermoplastic material of the required cross-section and to attach this to the main body which is also of thermoplastic material. This approach, while proving to be satisfactory, must be policed very carefully to ensure adequate quality control since separation of the parts is clearly unacceptable. As a result, the complexity of manufacture and the requirements for care and to ensure proper quality all add to the cost and complexity of the product.
This need related to catheters designed for intrusion into a blood vessel demonstrates the general need for a catheter having a tip of reduced cross-section of integral construction. Also a method of manufacture is needed which will permit a tip section of smaller cross-section to be formed integrally from part of the main body in a controlled manner so that the product is readily reproduced within acceptable tolerances.